Western leaders will be asked to pay a high price for Ankara’s help in crushing the jihadists.

The last time David Cameron visited Turkey, four years ago, he declared that « I am here to make the case for Turkey’s membership of the European Union ». Those pre–Arab Spring days seem a long time ago.

When Cameron meets President Recep Tayyip Erdogan in Ankara today, top of the agenda will be the raging civil war in nextdoor Syria, which has now killed more than 200,000 people – and the struggle against the jihadists of Islamic State (Isil), which is again taking place on Turkey’s southern flank.

But there is a curious thing about this second campaign. Although the United States is doing the heavy lifting, a motley crew of Arabs and Europeans are also pounding the jihadists on a daily basis. Yet while military minnows such as Bahrain and Belgium have sent warplanes, Nato’s only Muslim–majority member – located right on the edge of the action – is curiously absent. Why is Turkey sitting out this fight?

The Turks offer two answers. They complain, first, that attacking Isil is futile unless one also targets its cause: the Assad regime. They have a point. For more than a decade, the Syrian government has cooperated with jihadists to further its interests, for instance by funnelling fighters into Iraq to attack British and American troops after the 2003 invasion. In recent years, the regime deliberately allowed Isil to grow unchecked in northern and eastern Syria, realising – correctly – that it would weaken the mainstream opposition.

Turkey argues that the West’s narrow focus on Isil has benefited Assad on the ground, giving the appearance that the US is tacitly collaborating with the regime, and thereby pushing more of the opposition into the jihadists’ arms. Turkey is not alone in this view. Chuck Hagel, the outgoing US defence secretary, clashed with the White House on precisely this point, warning that America urgently needed « a sharper view of what to do about the Assad regime ».

Turkey’s second concern is related to Syria’s Kurds – who have, over the course of the civil war, carved out an autonomous territory across northern Syria called Rojava. Although Turkey’s relationship with the Kurds of Iraq is surprisingly friendly – Ankara is actually training their militia, the peshmerga – it views the leading Syrian Kurdish group as a branch of the separatist PKK, and worries that getting rid of Isil could inadvertently enable a hostile Kurdish bloc to crystallise on its doorstep.

With these concerns in mind, Turkey has made its participation in the war conditional on a fundamental shift in strategy. Its most specific demand is the creation of a buffer zone along the Turkish–Syrian border, protected from Assad’s troops and aircraft. Erdogan is certain to push this idea when he meets Cameron.

The stated aim of this buffer zone would be to protect civilians. But its downsides are threefold. First, depending on its scope, it would represent a serious escalation. The coalition has been ignoring Assad’s air defence network so far, but establishing a no–fly zone could involve destroying a good chunk of it through sustained cruise missile strikes and bombing raids. The presence of Russian « advisers » at the likely targets is a further complicating factor. Finally, artillery within the range of the buffer zone might also have to be targeted, which would mean a huge jump in the number of sorties.

Second, despite these costs, the safe zone might not accomplish much. If it only reaches 20 miles into Syrian territory, as reported, then it would mostly cover areas in which Assad’s influence is minimal – and wouldn’t get anywhere close to beleaguered cities such as Aleppo or Raqqa. It certainly wouldn’t change the balance of power in Syria.

Third, nuclear talks with Tehran are at an extremely delicate stage, and the US is obviously eager to secure Iran’s support for a managed political transition that removes Assad but preserves much of the Syrian state. The creation of a buffer zone would be seen by Iran as an invasion of a key ally, and it would respond accordingly.

Despite all this, it might nevertheless be worth the risk. The main benefit would be Turkey’s entry into the war – and, in particular, access to its crucial Incirlik airbase. Coalition pilots currently have to fly longer and trickier routes from the Gulf states 1,000 miles away, costing them six hours they could otherwise spend over their targets.

Turkey also seems to have promised to deploy its special forces on the ground, which would greatly increase the accuracy of the airstrikes against Isil and give a much–needed boost to the rebels staving it off. Contrary to common wisdom, and growing Western disillusionment, non–jihadist rebels do exist – and they comprise the only national force, albeit a dwindling one, aside from Assad and the jihadists.

Whether Turkey’s price is worth paying will ultimately be decided by one man: Barack Obama. But Britain also has a difficult decision to make. France has long supported a buffer zone, and could well become the first European state to carry out combat operations in Syria as well as Iraq. Does Cameron have the domestic political support to follow suit? His appetite for such escalation, just months from a general election, will play a large part in determining how he and President Erdogan get on today.

* Shashank Joshi is a senior research fellow at the Royal United Services Institute.